给我举例JAVA一个定时任务存储json字符串查询数据于一个字段的数据表编码

以下是一个JAVA定时任务存储JSON字符串并查询数据表的示例代码：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

import org.json.JSONObject;

public class JsonStorageTask extends TimerTask {

    private static final String DB_URL = "jdbc:mysql://localhost:3306/mydatabase";
    private static final String DB_USER = "root";
    private static final String DB_PASSWORD = "password";
    private static final String TABLE_NAME = "mytable";
    private static final String COLUMN_NAME = "json_data";

    private Connection connection;

    public JsonStorageTask() {
        try {
            connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void run() {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date now = Calendar.getInstance().getTime();
        String timestamp = dateFormat.format(now);
        JSONObject data = new JSONObject();
        data.put("timestamp", timestamp);
        data.put("value", Math.random() * 100);
        String jsonData = data.toString();
        storeJsonData(jsonData);
        queryJsonData();
    }

    private void storeJsonData(String jsonData) {
        try {
            String sql = "INSERT INTO " + TABLE_NAME + " (" + COLUMN_NAME + ") VALUES (?)";
            PreparedStatement statement = connection.prepareStatement(sql);
            statement.setString(1, jsonData);
            statement.executeUpdate();
            statement.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    private void queryJsonData() {
        try {
            String sql = "SELECT * FROM " + TABLE_NAME;
            PreparedStatement statement = connection.prepareStatement(sql);
            ResultSet resultSet = statement.executeQuery();
            while (resultSet.next()) {
                String jsonData = resultSet.getString(COLUMN_NAME);
                JSONObject data = new JSONObject(jsonData);
                System.out.println("Timestamp: " + data.getString("timestamp"));
                System.out.println("Value: " + data.getDouble("value"));
            }
            resultSet.close();
            statement.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Timer timer = new Timer();
        timer.schedule(new JsonStorageTask(), 0, 5000); // run every 5 seconds
    }

}

这个示例代码会在每5秒钟执行一次定时任务，生成一个JSON字符串并存储到数据库中，然后查询数据表并打印出来。JSON字符串中包含一个时间戳和一个随机数值。在存储和查询数据时，使用了预编译的SQL语句，可以防止SQL注入攻击。注意修改DB_URL、DB_USER、DB_PASSWORD、TABLE_NAME和COLUMN_NAME等常量的值以适配你自己的环境。